Stimulation of leptin release by actinomycin D in rat adipocytes

A greater understanding of the factors causing the enhanced release of leptin by adipocytes in obesity is needed. Experiments were designed to determine the effects of actinomycin D on leptin release by isolated rat adipocytes during primary culture for 24 hr. In adipocytes from fed hypothyroid rats, the initial rate of leptin release over the first 6 hr was not maintained over the next 18 hr. The decline in leptin release by adipocytes in primary culture between 6 and 24 hr was reduced markedly by either dexamethasone or actinomycin D. Both actinomycin D and dexamethasone also reduced the loss of leptin mRNA seen over the 24-hr incubation. Maximal effects on leptin release and leptin mRNA accumulation required only 0.1 microM of actinomycin D, a concentration that had no significant effect on the 18S RNA content of adipocytes at the end of a 24-hr incubation. In contrast to the reduced loss of leptin mRNA seen at 24 hr, the loss of glyceraldehyde-3-phosphate dehydrogenase messenger ribonucleic acid (GAPDH mRNA) was enhanced in the presence of 0.1 microM of actinomycin D. The effects of dexamethasone could be differentiated from those of actinomycin D by the finding that cycloheximide blocked the reduced loss of leptin mRNA due to dexamethasone while having no effect on that due to actinomycin D. These results point to a unique regulation of leptin release and leptin mRNA levels by actinomycin D.